Tandem vacuum booster with extensible bellow air sleeve

ABSTRACT

A tandem vacuum booster includes an internal air passage connection between primary and secondary high pressure chambers of the booster, and extending through a primary low pressure chamber of the booster. The internal air passage connection includes a tubular collar extending longitudinally from a divider separating the secondary high pressure and primary low pressure chambers, and an extensible air tube extending through and from a primary diaphragm of the booster, with the primary diaphragm defining the boundary between the primary high and low pressure chambers. The collar includes an outer surface thereof adapted for receiving a distal end of the extensible air tube extending over a portion of the outer surface of the collar. The distal ends of the collar and the air tube include elements for retaining and/or sealing the distal end of the extensible tube against the outer surface of the collar. The booster also includes a primary diaphragm support disposed for contacting a front surface of the primary diaphragm, and having a hole therein for passage therethrough of the extensible air tube, with the air tube including a locking bead on an outer surface thereof for engaging the primary diaphragm support around the hole, to thereby restrain movement of the extensible air tube relative to the diaphragm support and preclude chafing of the air tube that could occur if the air tube were not retained in the hole of the primary diaphragm support.

TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates to vehicle brake systems, and more particularly to tandem vacuum boosters for vehicle brake systems.

BACKGROUND OF THE INVENTION

[0002] Vehicles such as automobiles, trucks, buses, and motor homes typically include a dashboard at the front of the passenger compartment, having a power brake booster on the front of the dashboard connected by a push rod to a brake pedal mounted on the rear of the dashboard in the passenger compartment.

[0003] In one commonly used type of brake booster, known as a tandem vacuum brake booster, the booster includes a housing assembly, having a rear housing adapted for connection to the front of the dashboard, and a front housing adapted to receive and provide a mounting surface for a master cylinder of the brake system. The housing assembly of the vacuum booster includes a divider that divides the interior of the housing assembly into a primary and a secondary chamber, and provides sliding support for an axially movable booster piston that is connected via the push rod to the brake pedal.

[0004] Extending radially outward from the piston, in the secondary chamber of the housing, is a secondary diaphragm support. In similar fashion, a primary diaphragm support extends radially outward from the piston in the primary chamber. The primary and secondary diaphragm supports are fixed to the piston and move axially with the piston.

[0005] A flexible secondary diaphragm has an outer periphery sealed to the inner walls of the secondary chamber of the front housing, and an inner periphery sealed to the piston, to thereby form a secondary low pressure chamber between the secondary diaphragm and the front wall of the front housing and a secondary high pressure chamber between the secondary diaphragm and the divider.

[0006] A flexible primary diaphragm has an outer periphery sealed to the inner walls of the primary chamber of the rear housing, and an inner periphery sealed to the piston, to thereby form a primary low pressure chamber between the primary diaphragm and the divider, and a primary high pressure chamber between the primary diaphragm and the rear wall of the rear housing.

[0007] The booster includes valve elements, within the piston, for connecting all four chambers (i.e. the primary low pressure, secondary low pressure, primary high pressure, and secondary high pressure chambers) to a source of vacuum, such as the interior passages of an engine intake manifold, when the booster is operating in a release mode. When the brake pedal is depressed, the push rod moves the valve elements to a position where the primary and secondary low pressure chambers remain connected to the source of vacuum, but the primary and secondary high pressure chambers are connected to atmospheric air pressure around the brake booster.

[0008] The difference in pressure between the atmospheric pressure operating against the back face of the primary and secondary diaphragms, and the vacuum operating against the front side of the primary and secondary diaphragms, generates a force against the primary and secondary diaphragm supports that drives the piston forward, and augments the force exerted through the push rod from the brake pedal in moving the hydraulic piston in the master cylinder to generate hydraulic pressure in the brake system for applying the brakes. The action of the brake booster thus allows the pedal force required to generate a desired hydraulic pressure in the master cylinder to be significantly less than the pedal force that would be required without the booster.

[0009] The booster construction described above is compact and well suited to installation and operation in automobiles and trucks. Providing an internal air passage connection between the primary and secondary high pressure chambers can be difficult, however, because the internal connection must be routed either through or past the primary low pressure chamber. In addition to the difficulties involved in sealing an internal connection running through the primary low pressure chamber, the internal connection must also pass through the primary diaphragm support and the divider, and must be axially extensible and retractable to allow for axial movement of the primary diaphragm support relative to the divider, which remains stationary, as the booster piston moves within the housing.

[0010] In one prior approach to providing such an internal air passage connection running through the primary low pressure chamber, the primary diaphragm includes a flexible convoluted bellows air tube that extends from the primary diaphragm, through a hole in the primary diaphragm support, with the distal end of the tube having an annular groove in the outer surface of the tube that engages the edges of a hole in the divider, when the distal end of the tube is inserted into the hole in the divider. An adhesive may be required for securing the distal end of the tube in the hole in the divider.

[0011] This approach has several drawbacks, however. Forcing the distal end of the tube through the hole in the divider to engage the annular groove with the edge of the hole, and securing the distal end with adhesive are labor intensive, and require that the tube be compressed radially inward so that the outer periphery of the tube can be forced through the hole in the divider. Compressing a tube radially inward, and obtaining a good seal are difficult tasks. In addition, the air tube is not affixed to the primary diaphragm support, which may allow the tube to move back and forth in the hole through the primary diaphragm support, thereby causing chafing of the air tube against the edge of the hole in the primary diaphragm support.

[0012] What is needed, therefore, is an improved internal air passage connection between the primary and secondary high pressure chambers in a tandem vacuum booster of the type described above.

SUMMARY OF THE INVENTION

[0013] Our invention provides a tandem vacuum booster having an improved internal air passage connection between primary and secondary high pressure chambers of the booster, and extending through a primary low pressure chamber of the booster. The internal air passage connection includes a tubular collar extending longitudinally from a divider separating the secondary high pressure and primary low pressure chambers, and an extensible air tube extending through and from a primary diaphragm of the booster, with the primary diaphragm defining the boundary between the primary high and low pressure chambers.

[0014] The collar may include an outer surface thereof adapted for receiving a distal end of the extensible air tube, in a sealing relationship extending over a portion of the outer surface of the collar. The distal ends of either or both of the collar and the air tube respectively may include elements for retaining and/or sealing the distal end of the extensible tube against the outer surface of the collar.

[0015] The booster may also include a primary diaphragm support disposed for contacting a front surface of the primary diaphragm, and having a hole therein for passage of the extensible air tube, with the air tube including a locking bead on an outer surface thereof for engaging the primary diaphragm support around the hole, to thereby restrain movement of the extensible air tube relative to the diaphragm support and preclude chafing of the air tube that could occur if the air tube were not retained in the hole of the primary diaphragm support.

[0016] The foregoing and other features and advantages of our invention are apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawing. The detailed description and drawing are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWING

[0017] The drawing is a partial cross-section of an exemplary embodiment of a tandem vacuum booster according to my invention.

DETAILED DESCRIPTION

[0018] The drawing illustrates an exemplary embodiment of a tandem brake booster 10, according to our invention. The booster 10 includes a housing assembly 12, having a front housing 11 and a rear housing 13 thereof joined together and defining a longitudinal axis 14 of the booster 10. The housing assembly 12 has a divider 16 separating the interior of the housing assembly 12 into a secondary chamber 18 and a primary chamber 20, and providing sliding support for a booster piston 22 connected by a push rod to a brake pedal. The juncture of the booster piston 22 and the divider 16 is closed with a seal 24 that allows the booster piston to move back and forth along the longitudinal axis 14, as the brake pedal is depressed and released.

[0019] A secondary diaphragm 26 is attached at an inner periphery thereof to the booster piston 22 in the secondary chamber 18 of the housing assembly 12, and extends radially outward to an outer periphery thereof attached to the front housing 11. The secondary diaphragm 26 divides the secondary chamber 18 of the housing assembly 12 into a secondary low pressure chamber 28 bounded by the front housing 11, the piston 22 and the secondary diaphragm 26, and a secondary high pressure chamber 30 bounded by the piston 22, the secondary diaphragm 26, and a front face of the divider 16.

[0020] A primary diaphragm 32 attached at an inner periphery thereof to the booster piston 22 in the primary chamber 20 of the housing assembly 12, and extends radially outward to an outer periphery thereof attached to the rear housing 13. The primary diaphragm 32 divides the primary chamber 20 of the housing assembly 12 into a primary low pressure chamber 34 bounded by a rear face of the divider 16, the primary diaphragm 32, the front housings 11, and the piston 22, and a primary high pressure chamber 36 bounded by the rear housing 13, the piston 22, the primary diaphragm 32.

[0021] The divider 16 has a tubular collar 38 extending longitudinally therefrom into the primary low pressure chamber 34. The collar 38 defines an air passage conduit through the divider 16. The outer surface 40 of the collar 38 is adapted for receiving a sealing surface 54, 56 of an extensible air tube 42.

[0022] An extensible air tube 42 defines a air passage conduit through and extending longitudinally from the primary diaphragm 32 to a distal end 44 of the extensible air tube 42 that extends over and provides a sealing attachment to the outer surface 40 of the collar 38. In the exemplary embodiment, the extensible air tube 42 is formed integrally with the primary diaphragm 32, preferably from a material such as natural rubber. The extensible air tube 42 includes several annular convolutions 46, or longitudinally collapsible walls, disposed between the primary diaphragm 32 and the distal end 44 of the extensible air tube 42. These convolutions allow the air tube 42 to extend and contract longitudinally as the primary diaphragm 32, which is attached to and moves with the booster piston 22, moves longitudinally with respect to the divider 16, as the piston 22 is moved back and forth by the brake pedal being depressed and released.

[0023] The tubular collar 38 and extensible air tube 42 in combination form a longitudinally extensible air passage conduit passing through the primary low pressure chamber 34 and providing fluid communication between the primary and secondary high pressure chambers 36, 30 of the booster 10.

[0024] The distal end 44 of the extensible air tube 42 includes a thickened annular wall section 48, having a generally triangular cross section with one vertex 50 of the triangular cross section connected to the extensible air tube 42, a second vertex 52 of the triangular cross section forming an end of the extensible air tube 42, and the third vertex 54 of the triangular cross section forming a contact surface adapted for receiving and mating with the outer surface 40 of the collar 38. The triangular cross section provides several advantages for assembly and operation of the booster 10. The added material in the thickened wall area of the triangular cross section, together with the triangular configuration, allow the distal end 44 of the extensible air tube 42 to firmly grip the outer surface 40 of the collar, and provides for self-centering of the air tube 42 on the collar 38. The edge of the triangular cross section extending between the second and third vertices 52, 54 forms an angled ramp surface that facilitates sliding the distal end 44 of the air tube 42 over the outer surface 40 of the collar 38.

[0025] The distal end 40 of the extensible air tube 42 further includes a sealing lip 56 configured for pressure-biased sealing against the outer surface 40 of the collar by air pressure within the extensible air tube 42 and collar 38. The sealing lip 56 of the exemplary embodiment is attached to the triangular cross section of the distal end 44 of the air tube 42 at a point between the first and third vertices 50, 54. With the air tube 42 attached to the collar 38, the sealing lip 56 angles back from the end 44 of the air tube 42 toward the primary diaphragm 32, and the distal end of the sealing lip 56 rests against the outer surface 40 of the collar 38. Air pressure in the extensible air tube 42 acts on the radially outer surface of the sealing lip 56, and presses the sealing lip 56 more tightly against the outer surface 40 of the collar 38.

[0026] The distal end of the outer surface 40 of the collar 38 in the exemplary embodiment is flared and rolled back to form an annular bell-shaped, radially enlarged section 59 of the collar 38 for retaining the distal end 44 of the extensible air tube 42 in sealing contact with the outer surface 40 of the collar 38. The annular bell-shaped end 59 of the collar 38 serves as a retaining lip for engaging the thickened annular cross section 48 of the distal end 44 of the air tube 42. Specifically, the flared distal end of the collar 38 of the exemplary embodiment engages the distal end of the sealing lip 56 and holds the sealing lip 56 and the distal end 44 of the air tube in sealing contact with the outer surface 40 of the collar 38, and retains the end 44 of the air tube 42 on the collar 38 as the convolutions 46 of the air tube 42 extend and contract with movement of the piston 22 and primary diaphragm 32.

[0027] The booster 10 of the exemplary embodiment further includes a primary diaphragm support 58 attached to the booster piston 22 in the primary low pressure chamber 34, adjacent the inner periphery of the primary diaphragm 32 and extending radially outward from the piston 22 along a portion of a front surface of the primary diaphragm 32. The primary diaphragm support 58 serves to transfer force generated by the pressure difference across the primary diaphragm to the piston 22, for augmenting the force exerted on the brake pedal, and also serves to support and guide the primary diaphragm 32 as it moves in the primary chamber 20 of the housing 12. The primary diaphragm support 58 includes a hole 60 that allows the extensible air tube 42 to pass through the primary diaphragm support 58. The extensible air tube 42 has an annular locking bead 62 extending from the outer surface of the air tube 42, for longitudinally restraining the air tube 42 within the hole 60 of the primary diaphragm support 58 against longitudinal movement relative to the primary diaphragm support 58. Securing the air tube 42 to the primary diaphragm support 58 with the locking bead 62, in this manner, precludes having the outer surface of the air tube 42 becoming chafed by movement back and forth over the edge of the hole 60 in the primary diaphragm support 58.

[0028] While the embodiments of our invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. For example, in other embodiments of our invention, more than one collar 38 and extensible air tube 42 may be used, to form multiple internal air passage connections between the primary and secondary high pressure chambers 36, 30. The various elements and aspects of our invention may also be used independently form one another, or in different combinations than are described above and in the drawing with regard to the exemplary embodiment.

[0029] The scope of the invention is indicated in the appended claims. We intend that all changes or modifications within the meaning and range of equivalents are embraced by the claims. 

We claim:
 1. A tandem vacuum booster comprising: a housing defining a longitudinal axis of the booster, the housing having a divider therein separating the interior of the housing into a primary and a secondary chamber and providing sliding support for a booster piston; a booster piston supported by the divider for movement along the longitudinal axis; a secondary diaphragm attached at an inner periphery thereof to the booster piston in the secondary chamber of the housing and extending radially outward to an outer periphery thereof attached to the housing, to thereby define a secondary low pressure chamber bounded by the housing, the piston and the secondary diaphragm, and further defining a secondary high pressure chamber bounded by the piston, the secondary diaphragm, and a front face of the divider; a primary diaphragm attached at an inner periphery thereof to the booster piston in the primary chamber of the housing and extending radially outward to an outer periphery thereof attached to the housing, to define a primary low pressure chamber bounded by a rear face of the divider, the housing, the piston and the primary diaphragm, and further defining a primary high pressure chamber bounded by the housing, the piston, and the primary diaphragm; the divider having a tubular collar extending longitudinally therefrom into the primary low pressure chamber, the collar defining a air passage conduit through the divider and an outer surface of the collar for receiving a sealing surface of an extensible air tube; and an extensible air tube defining an air passage conduit through and extending longitudinally from the primary diaphragm to a distal end of the extensible air tube extending over and providing sealing attachment to the outer surface of the collar; the tubular collar and extensible air tube thereby forming a longitudinally extensible air passage conduit passing through the primary low pressure chamber and providing air passage communication between the primary and secondary high pressure chambers of the booster.
 2. The booster of claim 1 wherein the extensible air tube includes one or more annular convolutions disposed between the primary diaphragm and the distal end of the extensible air tube.
 3. The booster of claim 2 wherein the air tube includes two or more annular convolutions forming a bellows.
 4. The booster of claim 1 wherein the outer surface of the collar extending from the divider includes a radially enlarged section thereof for retaining the distal end of the extensible air tube.
 5. The booster of claim 4 wherein the distal end of the extensible air tube defines a retaining lip for engaging the radially enlarged section of the outer surface of the collar.
 6. The booster of claim 1 wherein the distal end of the extensible air tube includes a thickened annular wall section having a generally triangular cross section with one vertex of the triangular cross section connected to the extensible air tube, a second vertex of the triangular cross section forming an end of the extensible air tube, and the third vertex of the triangular cross section forming a contact surface adapted for receiving the outer surface of the collar.
 7. The booster of claim 6 wherein the distal end of the extensible air tube further includes a sealing lip configured for pressure biased sealing against the outer surface of the collar by air pressure within the extensible air tube.
 8. The booster of claim 7 wherein the distal end of the collar is flared to form a bell-mouth shape for retaining the sealing lip in contact with the outer surface of the collar.
 9. The booster of claim 8 where the sealing lip is attached at one end thereof to an inner surface of the distal end of the extensible air tube and extends from the inner surface of the distal end of the extensible air tube in a direction toward the primary diaphragm.
 10. The booster of claim 1 further comprising a primary diaphragm support attached to the piston in the primary low pressure chamber adjacent the inner periphery of the primary diaphragm and extending radially outward from the piston along a portion of a front surface of the primary diaphragm; the primary diaphragm support having a hole therethrough for passage of the extensible air tube; and the extensible air tube having a locking bead extending therefrom for longitudinally restraining the extensible air tube within the hole of the primary diaphragm support against longitudinal movement relative to the primary diaphragm support.
 11. A tandem vacuum booster comprising: a housing defining a longitudinal axis of the booster, the housing having a divider therein separating the interior of the housing into a primary and a secondary chamber and providing sliding support for a booster piston; a booster piston supported by the divider for movement along the longitudinal axis; a secondary diaphragm attached at an inner periphery thereof to the booster piston in the secondary chamber of the housing and extending radially outward to an outer periphery thereof attached to the housing, to thereby define a secondary low pressure chamber bounded by the housing, the piston and the secondary diaphragm, and further defining a secondary high pressure chamber bounded by the piston, the secondary diaphragm, and a front face of the divider; a primary diaphragm attached at an inner periphery thereof to the booster piston in the primary chamber of the housing and extending radially outward to an outer periphery thereof attached to the housing, to define a primary low pressure chamber bounded by a rear face of the divider, the housing, the piston and the primary diaphragm, and further defining a primary high pressure chamber bounded by the housing, the piston, the primary diaphragm; the divider having a tubular collar extending longitudinally therefrom into the primary low pressure chamber, the collar defining a air passage conduit through the divider and a surface of the collar for receiving a sealing surface of an extensible air tube; an extensible air tube defining an air passage conduit through and extending longitudinally from the primary diaphragm to a distal end of the extensible air tube providing sealing attachment to the surface of the collar; a primary diaphragm support attached to the piston in the primary low pressure chamber adjacent the inner periphery of the primary diaphragm and extending radially outward from the piston along a portion of a front surface of the primary diaphragm; the primary diaphragm support having a hole therethrough for passage of the extensible air tube; and the extensible air tube having a locking bead extending therefrom for longitudinally restraining the extensible air tube within the hole of the primary diaphragm support against longitudinal movement relative to the primary diaphragm support. the tubular collar and extensible air tube thereby forming a longitudinally extensible air passage conduit passing through the primary low pressure chamber and providing fluid communication between the primary and secondary high pressure chambers of the booster.
 12. The booster of claim 11 wherein the extensible air tube includes one or more annular convolutions disposed between the primary diaphragm and the distal end of the extensible air tube.
 13. The booster of claim 12 wherein the air tube includes two or more annular convolutions forming a bellows.
 14. The booster of claim 11 wherein the collar extending from the divider defines an outer surface of the collar for receiving an inner surface of the distal end of the extensible air tube.
 15. The booster of claim 14 wherein the outer surface of the collar further includes a radially enlarged section thereof for retaining the distal end of the extensible air tube.
 16. The booster of claim 15 wherein the distal end of the extensible air tube defines a retaining lip for engaging the radially enlarged section of the outer surface of the collar.
 17. The booster of claim 14 wherein the distal end of the extensible air tube includes a thickened annular wall section having a generally triangular cross section with one vertex of the triangular cross section connected to the extensible air tube, a second vertex of the triangular cross section forming an end of the extensible air tube, and the third vertex of the triangular cross section forming a contact surface adapted for receiving the outer surface of the collar.
 18. The booster of claim 17 wherein the distal end of the extensible air tube further includes a sealing lip configured for pressure biased sealing against the outer surface of the collar by air pressure within the extensible air tube.
 19. The booster of claim 18 wherein the distal end of the collar is flared to form a bell-mouth shape for retaining the sealing lip in contact with the outer surface of the collar.
 20. The booster of claim 19 where the sealing lip is attached at one end thereof to an inner surface of the distal end of the extensible air tube and extends from the inner surface of the distal end of the extensible air tube in a direction toward the primary diaphragm. 